A Cr--Cu--Cr (chromium-copper-chromium) multilayer film stack has been recognized as one of the more favorable structures for gas discharge panel, or plasma display panel (PDP) electrodes. In such an electrode, the Cu layer serves as the major current carrier. The bottom Cr layer is used to improve adhesion between the Cu layer and the glass substrate, panel or plate, while the top Cr layer protects the Cu layer from oxidation during later thermal manufacturing processes and serves as a reflective surface to reflect image light blocked by the electrode back into the plasma cell.
Cr--Cu--Cr multilayer films can be manufactured using a sputter deposition process. However, because sputtered Cr films have a metallic white color, the bottom Cr layer decreases the image contrast of the plasma display when reflecting ambient light back to viewer's eyes. To improve the contrast of the plasma display, an anti-reflective layer, also referred to in the art as a black matrix layer, can be deposited on the glass panel prior to the deposition of the Cr adhesion layer. The purpose of the black matrix layer is to reduce the amount of light reflected from the Cr surface.
An effective black matrix layer should have a dark color with a low reflectivity and a high light absorption. The black matrix layer should preferably be etchable with the proper chemical etchant, most preferably either the same etchant used to etch the Cr adhesion layer so that the anti-reflective layer can be etched together with the Cr adhesion layer, or an etchant that allows suitable selectivity to etch the metallic Cr and Cu layers. Further, the black matrix layer should provide good adhesion with both the glass substrate, panel or plate and the Cr adhesion layer.
Although any film meeting the above requirements can be used as a black matrix layer, the use of a film formed of a Cr-based compound is particularly advantageous. With Cr-based compounds it is possible to deposit the film using reactive sputtering and a pure Cr target. This allows the black matrix layer and the Cr adhesion layer to be deposited sequentially in the same chamber, eliminating the need for an independent black matrix layer deposition. Also, films formed of Cr-based compounds will generally provide etching properties similar to those of pure Cr films. This allows one to etch both the black matrix layer and adhesion layer in a single process step and negates the need for an additional etching step and the equipment needed to conduct the additional etching step.
A method of depositing a series of films of Cr, C and F by reactive sputtering, using a Cr metal target and an Argon-hexafluorethane (C.sub.2 F.sub.6) gas mixtures at various ratios, is disclosed in U.S. Pat. No. 5,628,882 to O'Keefe et al., the subject matter of which is incorporated herein by reference. (See also, Reactive Sputter Deposition of Crystalline Cr/C/F Thin Films, O'Keefe et al., Materials Letters 18 (1994) 251-256). The film composition (atomic percent) was in the range of (35-55) Cr, (20-25) C, and (20-45) F, and was controlled by varying the Ar:C.sub.2 F.sub.6 ratio. The films were determined to be crystalline and the composition was independent of substrate selection. Since PDP electrode applications were not considered in the patent, the film properties were not evaluated with regard to suitability for use as a black matrix layer
Accordingly, it is an object of the present invention to provide an effective black matrix layer that is compatible with a PDP electrode including a Cr/Cu/Cr film stack.
It is a further object of the invention to provide a black matrix layer that is integrated with the adhesion layer of a Cu-based PDP electrode.
It is another object of the invention to provide a method of forming an integrated black matrix/adhesion layer in a continuous sputtering deposition processes that can be performed in a single vacuum chamber.